Chapter 10 - Reaction Rates and Equilibrium

Question 1

How do you calculate the rate of a reaction?

Answer 1

Rate = change in concentration / time
(units = mol dm^-3 s^-1)

Question 2

What factors change the rate of a chemical reaction?

Answer 2

-Concentration
-Temperature
-Surface area
-Use of catalyst

Question 3

What is the collision theory?

Answer 3

The collision theory states that in order for a reaction to take place, two particles must collide with enough force

Question 4

What makes a collision effective?

Answer 4

-Correct orientation
-Enough energy to overcome the activation energy

Question 5

What effect does concentration have on rate of reaction?

Answer 5

When the concentration of reactants is increased, the rate of reaction will increase. This is because there are more particles in the same volume so the particles are closer together and collide more frequently, so there will be more successful collisions per unit time and an increased rate of reaction

Question 6

How does increasing pressure of a gas affect rate of reaction?

Answer 6

The rate of reaction will also increase as the same number of gas molecules occupy a smaller volume, so they are closer together and collide more frequently, so there are more successful collisions

Question 7

How do you measure the progress of a reaction?

Answer 7

-Measure decrease in concentration of reactants
-Measure increase in concentration of products

Question 8

What is a catalyst?

Answer 8

A substance that increases the rate of reaction without being used up. it does this by lowering the activation energy

Question 9

What is a homogeneous catalyst?

Answer 9

A catalyst that has the same physical state as the reactants. The catalyst reacts with the reactants to form an intermediate product, this then breaks down to form the final product

Question 10

What is a heterogeneous catalyst?

Answer 10

A catalyst that is in a different physical state than the reactants

Question 11

Why are catalysts often used in industry?

Answer 11

They reduce the temperature needed for the process and the energy required, this means less electricity / fossil fuels are used which can cut costs and increase profitability

Question 12

What does a Boltzmann distribution curve look like?

Answer 12

Question 13

How does the Boltzmann distribution curve change at higher temperatures?

Answer 13

-More molecules have energy greater than or equal to the activation energy
-Therefore more of the collisions will lead to a reaction, so the rate of reaction increases
-Collisions are also more frequent as the molecules are moving faster

Question 14

How does the Boltzmann distribution curve change with the use of a catalyst?

Answer 14

-A catalyst lowers the activation energy by providing an alternative route for the reaction so that a greater proportion on the molecules exceeds the lower activation energy

Question 15

What is dynamic equalibrium?

Answer 15

The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations do not change

Question 16

What is a closed system?

Answer 16

System that is isolated from its surroundings so the temperature, pressure and concentrations of reactants and products are unaffected by outside influences

Question 17

What is le Chatelier’s principle?

Answer 17

Le Chatelier’s principle states that when a system is in equilibrium subjected to external change the system readjusts itself to minimise the effects of that change

Question 18

What effect does change in concentration have on equlibrium?

Answer 18

-increasing the concentration shifts the equilibrium in the opposite direction:
If there are more products formed the position has shifted to the right and vice versa
e.g:
2A +3B —-> C + 2D
The position is shifted to the right as there are more moles of the left

Question 19

What effect does change in temperature have on equilibrium position?

Answer 19

An increase in temperature shifts the equilibrium position to the endothermic direction
A decrease in temperature shifts the position of equilibrium to the exothermic direction

Question 20

What effect does change in pressure have on equilibrium?

Answer 20

(only has effect if gases are involved)
Increasing the pressure of the system will shift the equilibrium to the side with less moles of gas

Question 21

What effect do catalysts have on the equilibrium position?

Answer 21

-No effect - they speed up both the forward and backwards reactions so the equilibrium position does not change